Growth of Vibrio parahaemolyticus on surfaces induces formation of a specialized bacterium called the swarmer cell. Differentiation to this cell type is controlled by an information transduction mechanism that couples perception of signals specific for life on a surface to expression of genes encoding the swarmer cell phenotype. The goal of this project is to understand how a bacterium senses its presence on a surface and conveys this information to the genes controlling swarmer cell development. In particular, we want to determine the signal transduction mechanism by which physical information is processed and converted to a signal reprogramming gene expression. The polar flagellum appears to function as the tactile sensor controlling swarmer cell differentiation by sensing forces that restrict its movement. Performance of one motility system (Fla) is linked to regulation of the second system (Laf). We propose to: 1, define the polar flagellar hierarchy of gene control, specifically to identify key Fla regulators and test their effect on Laf; 2, elucidate function of the sodium-type polar flagellar motor, i.e., to isolate and identify altered, impaired, add loss of function mutations and examine their effect on Laf; 3, extend our analysis of the structure, function, and regulation of the sheathed polar flagellum and correlate performance with Laf expression; and 4, define the Laf pyramid of control, in particular to identify the genes at the apex of the hierarchy and genes that control the apex. Our operating principle is that by genetically dissecting the two flagellar systems we will learn new, fundamental things about flagellar motility and in that process will genetically uncover the linkage between the two systems. Studying the two, interacting flagellar systems should help define general mechanisms of flagellar gene regulation, morphogenesis and function not yet elucidated, e.g., the mysteries of motor function (sodium channel function and chemomechanical coupling) and flagellum export and assembly. Moreover, studying surface- induced differentiation should reveal a novel mechanism of gene control and lead to an understanding of processes of surface colonization by many pathogens and other bacteria.